Fluid control systems for foils



Aug. 6, 1968 R. E. BOWLES FLUID CONTROL SYSTEMS FOR FOILS 6 Sheets-Sheet1 Original Filed Oct. 14, 1963 POL L 49/776 r TEHMSDWE :7 DEPTHINVENTOR. Eon 191.0 E. Bowuss 1968 R, E. BOWLES FLUID CONTROL SYSTEMSFOR FOILS 6 Sheets-Sheet 2 Original Filed Oct. 14. 1963 IN VENTOR.

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BY M 4 United States Patent Oflice Re. 26,434 Reissued Aug. 6, 196826,434 FLUID CONTROL SYSTEMS FOR FOILS Romald E. Bowles, 12712 MeadowoodDrive, Silver Spring, Md. 20904 Original No. 3,209,714, dated Oct. 5,1965, Ser. No. 316,000, Oct. 14, 1963. Application for reissue Feb. 14,1967, Ser. No. 628,511

32 Claims. (Cl. 114-665) Matter enclosed in heavy brackets II] appearsin the original patent but forms no part of this reissue specification;matter printed in italics indicates the additions made by reissue.

ABSTRACT OF THE DISCLOSURE Various parameters of the position ororientation of a foil in its environment are sensed on control flow offluid out of ports on the top and bottom and toward the rear of the foilto control lift forces on long adjacent surfaces of the foil tore-establish a desired position. Parameters sensed may be lift, depth,and angular rotation about one of the axes of the foil. Pure fluidamplifiers are employed which are responsive to fluid signals indicatingdeviation from a desired norm to control fluid flow to the ports.

The present invention relates to a fluid-operated, servocontrol systemfor controlling the lift of a foil supporting an air or water craftduring movement of the craft in the fluid medium.

Automatic pilots and servo-control systems of foil supported craftconventionally employ gyroscopes, accelerometers, electrical transducersand other types of sensing devices to monitor the position of the craftrelative to the free surface of the fluid medium on or in which thecraft is supported, or the position of the craft relative to someinertial reference plane. Computers and amplifying systems translate thesignals detected by these sensing devices to a common angle of attackcommand signal and this signal is applied to a mechanical actuator forchanging the angle of attack of one or more of the foils, therebyeffecting relocation or reorientation of the craft relative to thesurface of the medium or the inertial reference plane. Existingmechanical, electro-mechanical and electronic monitoring devices aregenerally delicate and require fine adjustment for proper operation andit would therefore be advantageous for many applications to eliminate asfar as possible moving mechanical elements and sensitive electronicdevices from the control system.

An inherent disadvantage common to conventional foil control systems isthe requisite necessity of converting or translating from one type ofenergy system to another type of energy system for effecting correctiveaction. For example, a conventional system for changing the angle ofattack of a foil typically comprises a device that monitors a fluidstatic pressure, circuitry that converts the pressure signal into anelectrical signal, with the electrical signal in turn energizing anelectro-mechanical device that reorients the foil in accordance with thesignal received thereby to correct the foil lift. It would be preferableif the pressure signal monitored could directly effect a change of foillift without further translation of the pressure signal to an electricalsignal and the electrical signal to a mechanical force for effecting achange of foil lift.

In accordance with the present invention, an air or water craft, as forexample a hydrofoil craft, is provided with a plurality of supportfoils, one or more of these foils being a servocd foil, and incorporatesmonitors or sensors responsive to certain conditions during movement ofthe craft on or through the water. Each servoed foil senses the liftconditions relative to the particular local dynamic conditions of themedium in which the foil is traveling and also senses the staticpressure at foil level as an indication of foil depth. The staticpressure is damped and time averaged by the static pressure sensor toeliminate the effect of higher frequency pressure fluctuations caused bychoppy water surface conditions. The lift and static pressure sensorsprovide fluid control signals which are combined with a fluid commanddepth signal, corresponding to the correct depth of the hydrofoil, toprovide an amplified fluid output signal that operates directly on thefoil by action or reaction to adjust its position, thereby to maintainthe depth and lift of the hydrofoil constant as it moves through thewater.

The control system may also be provided with fluid rate gyroscopes thathave no moving parts and yet produce an output signal in the form of afluid pressure or flow signal which is a function of the pitch and rollof the foil. These fluid signals are summed in a pure fluid amplifierwith the previously mentioned input control signals of the system toimprove the stability of the craft. The term fluid" includes liquid, gasand combinations of liquid and gas.

The system may also be provided with devices for controlling the liftcoefficient of the foil or foils during takeoff and crash diving duringwhich times the lift coefficients normally available are insufficient ortoo great to permit the desired maneuver.

Broadly therefore, it is an object of this invention to provide acontrol system for foils incorporating fluid devices having either aminimum, or no moving parts for the operation and control thereof.

More specifically, it is an object of this invention to provide a fluidcontrol system for controlling the lift of a foil, both during normalcruising conditions and extraordinary conditions, the control systemcomprising sensing, computing and amplifying systems, the computing andamplifying systems summing fluid signals received from sensing devicesand issuing a command signal for controlling the lift of the foil in thefluid medium through which the foil is moving.

Another object of this invention is to provide a fluid control system ofthe type described in the foregoing object for controlling theorientation of foils of subcavitating and supercavitating types.

The above and still further objects, features and advantages of thepresent invention will become apparent upon consideration of thefollowing detailed description of several specific embodiments thereof,especially when taken in conjunction with the accompanying drawings,wherein:

FIGURE 1 of the accompanying drawings illustrates a sectional side viewof a foil attached to a hydrofoil craft and, in addition, schematicallyshows control systems for varying the angle of attack of the foil;

FIGURE 2 illustrates a fluid computing and amplifying system employingfluid signals derived from various fluid monitoring devices responsiveto the depth of the foil below the surface of the medium, orientationdynamics of the craft and fluid dynamic characteristics of the mediumsurrounding the foil;

FIGURE 3 is a plan view of a typical pure fluid pressure amplifierutilized in the fluid amplifying and computing system of this invention;

FIGURE 4 illustrates a sectional side view of a probe incorporating apure fluid lift sensing and measuring system;

FIGURE 5 illustrates a system for sensing the static pressure at therunning depth of the foil, the fluid signal produced by the system beingcompared to that of a preselected running depth signal so that therunning depth of the foil can be changed until it is at the preselecteddepth;

FIGURE 6 illustrates an embodiment of the present invention, wherein thefluid from the pure fluid computing and amplifying system incorporatedin a foil produces reactive and pressure effects for altering theposition of the foil in the medium;

FIGURE 7 is a sectional side view of a supercavitating type of foilincorporating the fluid control system of the instant invention forcontrolling the lift of the foil;

FIGURE 8 is a sectional side view of a foil incorporating anotherembodiment of the fluid control system of this invention; and

FIGURE 9 is a perspective view of a hydrofoil craft employing threeindependently servoed hydrofoils.

Referring now specifically to FIGURE 1 of the drawings for a morecomplete understanding of the invention, there is illustrated an air orhydrofoil 10 intended to be propelled in the direction of the arrow D.The foil 10 is mounted for pivotal movement to a strut 11 by means of apivot pin 12 having the ends thereof secured in the foil 10. The pin 12is preferably located just forward of the center of pressure of the foil10 and the strut 11 is afiixed to the bottom of a body or craftindicated generally by the reference numeral 13, which is to be supported in a fluid medium by two or more foils of similar configurationto that of the foil 10. For the sake of simplicity of explanation, thecontrol system for a single foil is described in detail, although it isto be appreciated that the fluid control system of this invention mayalso control the remaining foil or foils employed for supporting thecraft 13.

As to the number of foils associated with any particular craft, variousfoil arrangements are presently provided. A particular craft may employa single large foil toward the bow and a smaller foil toward the stern.The stern foil would preferably be servoed in accordance with thepresent invention. A craft may employ two transversely aligned foilstoward the bow and a single servoed foil in the rear. The two forwardfoils may be servoed instead. Alternatively, all three foils may beservoed as subsequently described. On a large vessel, four or more foilsmay be employed in rows along the sides with all foils servoed.

Returning to FIGURE 1, the center of pressure of the foil 10 ispreferably displaced a relatively short distance from the pin 12 in adirection opposite that of the arrow D, a distance great enough toinsure stability of the foil 10 during movement through the medium 14,and yet located sufficiently close to the pin 12 so that undesirabletorque amplitudes are not developed about the pin 12 by foil flutter orlift forces. The foil 10 is formed by upper and lower surfaces referredto by the numerals 16 and 17, respectively, the surfaces tapering fromthe leading edge of the hydrofoil to the trailing edge to provide, forexample, a conventional, subcavitation type of foil.

Extending forward of the leading edge of the foil 10 is a lift sensor20, FIGURE 1, for supplying fluid signals corresponding to forces oflift predicted by the sensor to a pure fluid control system 21preferably housed within the foil 10. The fluid control system 21supplies differential fluid pressure signals to upper and lower servochambers 22 and 23, respectively, of a servo unit 19 embodied in thefoil 10. A dividing wall 24 is affixed to the hydrofoil 10. A dividingvane 32 is rigidly attached to strut 11 providing a fixed wall betweenthe upper and lower servo chambers 22 and 23, respectively. A dividingor island member 24 is designed so that fluid from the servo unit 19egresses into a venting passage 25. Fluid egressing from the passage 25discharges to the surrounding fluid medium 14 or into a sump (notshown).

In addition to the lift sensor 20 and a depth sensor 26 which areresponsive to variations in different parameters of foil positionrelative to the fluid medium, there is provided a depth command signalsource 27 and a pitch and a roll rate transducer referred to generallyby numeral 28 which monitor pitch and roll rate of the craft 13. Each ofthe above elements develop fluid control signals for controlling theoperation of the pure fluid control system 21 in response to variationsdetected in various parameters to be monitored. The depth command signalsource 27 may be housed in the craft 13 and the pitch and roll ratetransducer 28 may be housed either in the craft 13 or the transducersmay be attached to the strut 11. The signals from the various monitoringsystems are received and combined by the control system 21.

The fluid output signals issuing from the pure fluid control system 21are received by output passages 30 and 31 formed in the foil 10, thepassages 30 and 31 terminaing in essentially opposed outlets for issuingfluid into the upper and lower (as illustrated in FIGURE 1) servochambers 22 and 23, respectively. A dividing vane 32 is fixedlyconnected to the strut 11, the width of the vane 32 being substantiallyequal to the width of the chambers 22 and 23 so that pressuredifferentials in the chambers 22 and 23 produce pivotal movement of thefoil 10 relative to the strut 11 about the pin 12. For example, if theOutput passage 30 receives fluid at a greater pressure than the outputpassage 31, the pressure in the chamber 22 exceeds that of the chamber23, and the resulting build-up in pressure in the chamber 22 tends toproduce counterclockwise pivotal movement of the foil 10 about the pin12. Constriciions 34 are formed in the channels between the divider 24and the spaced adjacent walls of the foil 10 so as to permit pressure tobe developed in the chambers 22 and 23. The constrictions, however, mustnot be great enough to inhibit relatively rapid outflow of fluid sothat, upon reduction or increase in flow to a chamber, the pressure inthe chamber may rapidly adjust to the new condition.

Referring now to FIGURE 2 of the accompanying drawings, there isillustrated in detail the control system 21 of FIGURE 1 and includes sixpure fluid amplifiers, the amplifiers being respectively designated asA1, A2, A3, A4, A5 and A6, included in the pure fluid control system 21.Since pure fluid amplifiers form an essential element in the controlsystem of the present invention, it is necessary to understand thenature and operation of a typical pure fluid amplifier, To this end,reference is directed to FIGURE 3, wherein a single pure fluid summingamplifier 39 is illustrated.

The pure fluid summing amplifier 39 is preferably formed as asandwich-type structure of three flat plates 40, 41 and 42, sealedtogether in a fluid-tight relationship by means of adhesives, machinescrews or any other suitable means. The middle plate 41 is molded,etched or otherwise formed to provide channels in at least one surfacethereof to provide the configuration shown in FIG- URE 3. The plates 40and 42 serve to confine fluid flow in the pure fluid summing amplifier39 to one plane. The channel configuration formed in the plate 41provides a power nozzle 43, generally opposed control nozzles 44, 45 and46, 47, a fluid interaction chamber 48, having sidewalls 49 and 50 setback remotely from the outlet orifice of the power nozzle 43, and threeoutput passages designated by the numerals 54, 55 and 56 positioned toreceive fluid passing through the interaction chamber 48. A pair ofopenings 57 and 58 are provided in the plate 40 contiguous with thesidewalls 49 and 50, respectively, the openings 57 and 58 being boredthrough the plate 40. The openings 57 and 58 discharge fluid receivedinto a sump (not shown) or to an ambient pressure environment and serveto defeat boundary layer effects and insure that equal pressures aremaintained on opposite sides of the power stream flowing into thechamber 48 except for those pressures resulting from fluid flow from thecontrol nozzles 44, 45, 46 and 47.

The pure fluid summing amplifier 39 is preferably symmetrical withrespect to a centerline CL taken through the center output passage 55and the power nozzle 43, as shown. Tubes 60, 61, 62, 63, 64, 65, 66 and67 may have the ends thereof threadedly connected into threaded holesformed in the plate 42, and supply and receive flud from the amplifier39, the tubes 60, 61, 62, 63 and 64 supplying fluid to the amplifier 39and the tubes 65, 66 and 67 receiving fluid from the amplifier, i.e.,passages 54, 55 and 56, respectively. The extensions or sections of alltubes are indicated by dotted lines, as illustrated in FIG- URE 3.

The operation of pure fluid summing amplifier is now well known to thoseworking in the art and, for this reason, it suflices to state that amain or power stream is received by the tube 60 and issues from thepower nozzle 43 as a well-defined stream into the interaction chamber48. Control fluid streams may be received by any or all the tubes 61,62, 63 and 64 and these fluid streams issue as control streams from thecontrol nozzles 44, 45, 46 and 47, respectively, to interact with, andthereby effect amplified directional displacement of the power stream inthe interaction chamber 48. If the control nozzles 44, 45, 46 and 47 areall issuing equal magnitude fluid control streams in interactingrelationship with the power stream, or if there is no control fluidinput supplied to any of these control nozzles, the power stream flowsmainly into the center output passage 55 and issues from the tube 66.Due to the fact that there is some spreading of the power stream, equalportions thereof flow into the passages 54 and 56. The tube 66 ispreferably connected to a sump or ambient pressure environment for thisapplication and the fluid signal from the tube 66 is therefore notgenerally utilized as an output signal. The displacement of the powerstream issuing from the power nozzle 43 in the interaction chamber 48 iseffected by differentials in pressure between control streams issuingfrom opposed control nozzles. For example, the power stream is partiallyor substantially completely deflected into the output passage 56 if oneor both of the control nozzles 44 and 46 issues a control fluid streamhaving a pressure greater than that applied by the fluid stream orstreams issuing from the control nozzles 45 and/ or 47.

Conversely, the power stream is partially or substantially completelydisplaced into the output passage 54, if, singly or in combination, thecontrol nozzles 45 and 47 produce a momentum transverse of the powerstream in the interaction chamber greater than that produced by fluidissuing from the control nozzles 44 and 46 singly or in combination. Aswill be evident, the differentials in pressure between the outputpassages 54 and 56 depend upon the deflection of the power stream byfluid control streams, the angle of deflection being a function of thedifferences in control flow on opposite sides of the stream.

Since the power stream has a considerably greater momentum than thefluid of any of the control streams, and since the smaller momentumcontrol streams effect displacement of the power stream, amplificationas well as summation of fluid control signals is achieved by controlstream displacement of the power stream in the pure fluid summingamplifier 39. Although two pairs of control nozzles are illustrated inFIGURE 3, a single pair of opposed control nozzles may alternatively beused in those applications where only two sets of control fluid pressuresignals are to be summed and amplified. A more detailed disclosure ofpure fluid pressure amplifying systems of the type described brieflyhereinabove may be found in US. Patent No. 3,024,805 issued to B. M.Horton. Since it is an objective of this invention to reduee as far aspossible the number of moving parts required in the control system, purefluid amplifiers are preferable to other types of amplifiers since theyprovide pressure signal summation and amplification without employingany moving mechanical parts.

Referring again to FIGURE 2 of the drawings, output tubes or passages 70and 71 of the fluid amplifier A1 are connected to control nozzles 72 and73 of the fluid amplifier A2 and the output tubes 74 and 75 of theamplifier A2 are connected to control nozzles 76 and 77, respectively,of the fluid amplifier A4. The output tubes 80 and 81 of the amplifierA3 are connected to the control nozzles 82 and 83, respectively, of theamplifier A4, and the output tubes 84 and 85 of the amplifier A4 areconnected to control nozzles 86 and 87, respectively, of the amplifierA5. The output passages 88 and 89 of the amplifier A5 are connected tosupply fluid to the output passages 30 and 31, respectively, and to thetubes 188 and 189, respectively. The passages 30 and 31 supplydifferential fluid pressures to the upper and lower chambers 22 and 23,FIGURE 1, of the servo unit 19, FIGURE 1, whereas a second set of outputtubes 188 and 189 of amplifier A5 are connected to supply fluid controlsignals to control nozzles 186 and 187, respectively, of the amplifierA6.

The amplifiers A1, A2, A3, A4, A5 and A6 are provided with power nozzles90, 91, 92, 93, 94 and 191, respectively, for supplying power streams tothe interaction chambers of the amplifiers. As will be apparent to thoseworking in the pure fluid amplifying art, the amplifiers A2, A4 and A5may be staged and so designed that the power nozzles 91, 93 and 94,respectively, receive increasing magnitude power streams so thatsuccessively increasing pressures are produced by each of theseamplifiers. The same result may be obtained even though the samepressure is supplied to all power nozzles if the amplifiers are suitablydesigned as to configuration and size. The system employing identicalamplifiers and increasing supply pressures is employed for ease offabrication. Fluid for the power nozzles 90, 91, 92, 93, 94 and 191,inclusive, may be supplied to those power nozzles through tubing fromsources (not shown) of pressurized fluid housed in the craft 13, thestrut 11 being provided with suitable channels to enclose such tubing.With reference to the amplifier A1, it can be seen that the controlnozzles 96 and 97 of this amplifier receive fluid control signals fromthe lift sensor 20. The lift sensor 20 is utilized to predict forces oflift acting on the foil 10 and the differential output signal of thelift sensor is proportional to the product of the dynamic pressure andthe angle of attack of the foil 10 relative to a preselected referenceaxis or plane. Since it is highly advantageous to reduce the number ofmoving mechanical ports in the foil control system and to eliminate theneed for converting from one type of energy to another, the lift sensor20 illustrated in FIGURE 4 of the drawings is preferable to conventionaltypes of lift sensors.

Feferring new to FIGURE 4, the lifter sensor 20 is incorporated in aprobe 100 which is rigidly attached to the lower surface 17 of the foil10 in the embodiment illustrated. A servoed sensor, movable with respectto foil 10, may be employed for purposes to be explained subsequently.As the probe 100- and foil 10 move through a fluid medium, for instanceWater, forces of lift are received by the craft 13 and the direction ofthese forces depends upon the angle of attack (a) of the foil 10relative to some reference axis or plane, designated by the line 3-8 andestablished by relative motion of the foil 10 through the fluid medium14. The angle of attack (a) is taken as positive in FIGURE 4 since thelift forces developed by movement of the foil through the water tend tourge the foil 10 upwardly whereas negative angles of attack (a) tend tourge the foil 10 downwardly deeper into the water. The lift of mostfoils is proportional to the product of the angle of attack (a) and thefree-stream, dynamic pressure caused by movement of the foil through thewater over the range of angles of attack (or) encountered in normaloperation.

The lift sensor is adapted to sense the magnitude or amplitude of liftforces developed on the foil 10 during movement through water and toprovide differential output signals proportional thereto. The outputpressure signals from the sensor 20 are measured and amplified byapplying the signals to a pure fluid amplifier A7, the pure fluidamplifier A7 being of the aforedescribed stream interaction type.

The cavities, passages and nozzle needed to provide the pure fluidsensor 20 may be easily formed in a flat plate 101 by the methodsdescribed previously in regard to the forming of pure fluid amplifiers,and the plate 101 is t sealed between flat plates 102 and 103 in afluid-tight relationship. Since the cavities, passages and nozzle of thesensor 20 are formed by a sandwich-type construction, the plates formingthe passages, etc. of the sensor 20 may also form the amplifier A7 sothat the amplifier and sensor passages are combined in a singlesandwich-type structure, as shown in FIGURE 4. For the purposes ofclarity, the plates 101, 102 and 103 are shown to be composed of a clearplastic material; however, it should be understood that any materialcompatible with the working fluid may be employed.

The amplifier A7 comprises a power nozzle 104, a pa'r of substantiallyopposed control nozzles 105 and 106, an interaction chamber or region107, output passages 108, 109 and 110, and flow outlets 111 and 112. Thetubes 113, 114 and 129 receive fluid from the outlets 111, 112 and 109,respectively, and discharge fluid so received into the fluid medium 14or into a sump (not shown). A constant pressure supply source 69, FIGURE5, supplies fluid to the power nozzle 104 by means of a tube 115.

The lift sensor 20 includes a nozzle 116 receiving fluid filtered ofextraneous matter by filter 69a and at constant pressure from the source69, FIGURE 5, by means of a tube 117. The nozzle 116 discharges fluidinto a transverse tube 118 having tube constrictions 119 and 120 formedtherein adjacent the discharge end thereof, the constrictionsrestricting flow from the tube 118. Flow from the tube 118 egresses intoa parallel tubing system comprising a pair of equi-diametered tubes 121and 122, the constrictions 119 and 120 isolating the pressure in tube118 from pressure variations in tubes 121 and 122. One end of each ofthe tubes 121 and 122 terminates in control nozzles 105 and 106,respectively, of the amplifier A7, the other ends terminating inequi-diametered ports 125 and 126, respectively. A pair of porous plugs127 and 128 are inserted into the tubes 121 and 122, respectively, forproviding resistance to flow from the tubes 121 and 122. The tubes 121and 122 could be provided with other types of fluid resistances such asconstrictions or nozzles as alternatives to porous plugs.

The resistance to flow provided in the tubes 121 by the fluid resistance127, port 125 and nozzle 105 and in the tube 122 by the fluid resistance28, port 126 and nozzle 106 permits the development of relatively highpressures in each of the tubes 121, and 122, respectively. The pressuresin these tubes vary directly as the backloading pressures exerted on thelift sensor 20 at the ports 125 and 126. Preferably, the amplitude ofthe supply pressure received by the nozzle 116 is great enough so thatflow always egresses from the ports 125 and 126 during operation of thesensor 20, the amount of flow egressing independently from each of theports 125 and 126 being dependent upon the external pressures developedby the fluid medium 14 at the ports 125 and 126, respectively.

The lift force developed by the foil 10 is proportional to the productof the angle of attack (or) relative to the reference axis BB and thedynamic pressure developed as a result of motion of the foil through thefluid medium 14. These are the same factors that determine thebackloading on ports 125 and 126 so that the differential in pressuresensed at the ports 125 and 126 is a function of the lift developed bythe foil 10. This function may be made a linear function if the ports125 and 126 are properly positioned with respect to the leading surfaceof the probe 100. The linearity of the function holds for certain rangesof angle of attack (a) variation with respect to the reference axis BBof the foil 10.

It is desirable that the lift be maintained relatively constant eventhough the foil is subjected to varying angles of attack and dynamicpressures as it passes through waves in the fluid medium 14.

Expressing this empirically, the lift is equal to the product of somefunction of dynamic pressure and some function of the angle of thesensor relative to the flow pattern of the fluid surrounding the sensorimmediately in front of the foil. If the dynamic pressure varies due toa change in speed of the craft, wave motion, changes in velocity of thesurounding currents, etc. then the lift changes; and this is sensed as avariation in the differential in pressure in passages 121 and 122. Thus,the gain of the sensor as related to angle of attack is a function ofdynamic pressure. If the angle of attack changes due to change inposition of the foil in the fluid medium, changes in direction of thecurrents, etc., the lift changes; and again, this is detected as achange in the differential in pressure between channels 121 and 122.

Assume for the purpose of explanation that the angle (a) is desired tobe maintained zero and that, under this condition, the ports 125 and 126are symmetrical with respect to the axis BB. Both ports are equallybackloaded when angle (a) is zero; the dynamic pressure has no effectsince it determines the gain of the sensor; and a null out put pressuredifferential appears across the passages of the amplifiers A7 and A1.This null output signal will not affect the displacement of the powerstreams in any of the amplifiers A7, A1, A2, A4, A5 or A6, inclusive.With a change of angle (a), for instance, to a positive angle of attack,the port 125 is exposed to a greater pressure than the port 126 causinga greater backloading of flow from the tube 121 than the new backloadingof flow from the tube 122. Since the nozzle 116 supplies fluid atconstant pressure to the tube 118 and hence substantially equal flows totubes 121 and 122, the increase in back pressure applied to tube 121combined with the decrease in back pressure applied to tube 122 causesmore fluid to issue from the control nozzle than issues from the controlnozzle 106. The gain parameter, dynamic pressure, determines thedifferential signal level actually produced by the gain change in angleof attack. The difference in the fluid flows from nozzles 105 and 106displaces the power stream in the amplifier A7 from the passage 109 sothat a greater portion flows into the passage and the output tube 123athan flows in the passage 108 and the output tube 123.

Referring now to FIGURE 2 and to the amplifier Al, the output tube 123ais connected to the control nozzle 96 and the output tube 123 isconnected to the control nozzle 97 of that amplifier so that the powerstream issuing from the power nozzle 90 of the amplifier is displacedwhereby a greater quantity of fluid is received by the output tube 71than is received by the output tube 70. This in turn causes a greaterquantity of control fluid to issue from the control nozzle 73 of theamplifier A2 than issues from the control nozzle 72. Thus, the powerstream issuing from the power nozzle 91 of the amplifier A2 is displacedto supply a greater quantity of fluid to the output tube 74 than issupplied to the output tube 75, assuming null or equal amplitude controlsignals from the sensor 26 and the source 27. The corresponding controlnozzles 76 and 77 of the amplifier A4 thereupon receive correspondingdifferential pressure control signals so that a greater propor tion ofthe power stream issuing from the power nozzle 93 in the amplifier A4 isdisplaced into the output tube 85 producing a pressure in the controlnozzle 87 of the am plifier A5 greater than that in the control nozzle86. The larger magnitude control stream issuing from the control nozzle87 displaces a greater proportion of the power stream issuing from thepower nozzle 94 of the amplifier A5 into the output passage 88 and thispressure is received by the passage 30 whereupon the pressure in theupper chamber 22 increases to a value above the pressure of the lowerchamber 23. This differential in pressure between the upper and lowerchambers causes counterclockwise pivotal movement of the foil about thepin 12, as discussed previously, so that the angle of attack (a), FIGURE4, is decreased to some predetermined value, for instance, zero.

Conversely, if the port 126 is exposed to a greater pres sure than thatsensed by the port 125, the control nozzle 106 of the amplifier A7issues a greater magnitude control stream than that issuing from thecontrol nozzle 123 so that the power stream issuing from the powernozzle 104 is displaced into the output tube 108. The differential inpressure appearing across the output tubes 123 and 123a is transmittedthrough the fluid amplifying system A1, A2, A4, A5, resulting in anincrease in pressure in the lower chamber 23 of the servo unit 19 sothat the foil is pivoted clockwise about the pin 12 to effect acorrective change in the angle of attack (11) thereby increasing thelift of the foil and decreasing the pressure sensed by the port 126until both ports 125 and 126 sense equal pressures indicating zero angleof attack.

The lift sensor 20 in conjunction with the control system 21 and theservo unit 19 function as described to insure that the foil 10 developsa constant lift during movement through the water.

As disclosed in greater detail in co-pending US. patent applicationSerial No. 359,758, filed April 14, 1964, by Richard S. Windsor andmyself, and entitled Fluid Lift Sensing and Measuring System, therelationship between the forces of lift sensed and the output pressuresignals which issue from the output tubes 123 and 123a may be a linearfunction for optimum locations of the ports 125 and 126 relative to thechord length of the probe 100. This relationship is ordinarily desirablebecause it obviates problems of sensor and amplifier design that areencountered when the relationship is non-linear. Linearity of pressurewith angle of attack may be attained for values of (a) in a range offrom i6 toi20", depending upon the particular design of the sensor. Allof the sensors have basic similarities in design and are provided withfaired surfaces continuous from the leading to the trailing edges withthe ports located between 2 percent and 20 percent of the chord lengthof the probe from the leading edge of the probe.

It will be noted that movement of the foil 10 with the sensor 20attached thereto tends to increase the signal produced by sensor 20during repositioning of the foil. For instance, if lift is greater thandesired, the pressure in passage 121 is larger than in passage 122 andcommands counterclockwise rotation of the foil and sensor. Downward(counterclockwise) movement of the sensor 20 tends to increase thepressure at orifice 125 and to decrease this factor at the orifice 126.Thus, the pressure differential between passages 121 and 122 isincreased and may tend to produce overshoot and hunting of the foilabout the desired final position.

As previously indicated, the sensor 20 may be supported for movementrelative to the foil 10 and the support may be such as to eliminate theproblems referred to above. Thus, the sensor may be pivotally supportedon an arm or arms with the pivot point being located ahead of theleading edge of the sensor. The output passages 123 and 123a wouldsupply signals to amplifier A1 of FIGURE 2 and the sensor ismechanically coupled to the foil so that the sensor 20 is moved to anangle of attack equal to that of the foil. Since the pivot point of thesensor 20 is forward thereof, a signal calling for decrease in angle ofattack would cause the sensor to pivot counterclockwise; that is, moveupward in FIGURE 1. During movement of the sensor, the pressure on port126 is increased, thereby reducing the original command signal andpreventing overshoot and subsequent hunting of the foil.

The static pressure sensor 26 and the depth command signal source 27 areshown schematically in FIGURES l and 2 as supplying fluid controlsignals to the control nozzles 148 and 149, respectively, of theamplifier A2 so as to effect amplified displacement of the power streamissuing from the power nozzle 91 of that amplifier. The sensor 26 may beof any conventional type which detects the static pressure head on thefoil 10 as it moves through the medium 14 and produces a fluid outputsignal corresponding to foil depth. The depth command signal source 27may also be of conventional design, taking the form of an adjustablevalve 130, FIGURE 5, which receives fluid at constant pressure from afiltered supply 131. By adjustment of the valve 130, the control nozzle149 receives a pressure bias that is directed to oppose variations incontrol stream flow from the control nozzle 148. Thus, the depth of thefoil 10, as ascertained by the depth sensor 26 can be compared with thedesired depth as established by the pressure of the fluid issuing fromthe depth command source 27 to effect a displacement of the power streamissuing from the power nozzle 91 of the amplifier A2 corresponding tothe difference between the commanded and actual depth. Thus, if thedepth of the foil 10 increases beyond that limit set by the signalsource 27, the control nozzle 148, FIGURE 2, effects displacement of thepower stream 91 into the output tube 75. The control nozzle 77 of theamplifier A4 effects displacement of the power stream issuing from thepower nozzle 93 into the output passage 84 and hence into the controlnozzle 86 so that the power stream issuing from the power nozzle 94 ofthe amplifier A5 is displaced into the output passage 89, passage 31 andhence, into the lower chamber 23 of the servo unit 19 so that the foil10 is rotated in a clockwise direction about the pivot 12 therebyraising the leading surface of the foil 10, increasing the liftdeveloped thereby and decreasing the running depth of the foil 10 in themedium 14. Conversely, if the depth sensor 26 receives a static pressuresignal less than the depth command signal issuing from the source 27,the power stream issuing from the power nozzle 91 in the amplifier A2will be displaced into the output tube 74 ultimately causing an increasein pressure in the upper chamber 22 of the servo unit 19 and consequentpivotal movement of the foil 10 in a counterclockwise direction aboutthe strut 11, so that the angle of attack of the foil is decreased todecrease lift and increase the running depth of the foil 10.

The depth sensor 26 may be of any conventional type. However, if it isdesired to minimize mechanical moving parts in the control system of thefoil 10, the sensor 26 illustrated in FIGURE 5 of the drawings providesa fluid system having a minimum number of moving mechanical partscapable of producing a fluid output signal corresponding to variationsin depth of the foil in the medium 14.

As disclosed in more detail in my co-pending application No. 336,677,filed January 9, 1964, the sensor 26 includes an elongated probe 132,fixed to and located at a position on the strut 11 where it is desiredto sense and measure the static pressure of the medium supporting thecraft 13. The longitudinal axis of the probe 132 is positionedapproximately parallel to anticipated lines of medium flow as shown bythe arrows in the figure.

The probe 132 is provided with a series of ports referred to by thenumeral 133, the ports being spaced at predetermined intervals aroundthe periphery of the probe so that the ports sense the average of staticpressures of the medium around the probe 132 at any instant in time. Theaxes of the ports 133 are essentially perpendicular to the longitudinalaxis of the probe 132 so that the effects of dynamic fluid pressure areminimized. The ports are joined by a manifold 134 which is connected toone end of a tube 136. This end of the tube 136 is provided with a fluidresistance or constriction 135 for restricting flow from and into themanifold 134. The fluid resistance 135 may take the form of a porousplug, or the orifices of the ports 133 may serve this function if thetotal crosssectional area of the ports is smaller than that of the tube136. The tube 136 receives pressurized fluid from an upper chamber 137of a fluid capacitance 138.

The term fluid capacitance as used herein may be defined as that classof fluid energy storage means that store the energy of fluid aspotential energy, and in general, the energy stored in a fluidcapacitance increases as the quantity of fluid received increases. Afluid capacitance may take one or more of the following exemplary forms:compression of a fluid to a greater density than its normal density,change of thermodynamic state of a fluid, change of fluid internalenergy level, compression of one fluid by another fluid separated fromthe first fluid by a flexible diaphragm or wall, compression of a secondfluid in direct contact with a first fluid, deformation of elastic orflexible walls which restrain the fluid, change in elevation of thefluid or change of elevation of a plate supported by the fluid.

The term *fluid" as used herein includes compressible as well asincompressible fluids, fluid mixtures and fluid combinations such as airand water. When compressible fluids are used, a fluid capacitance neednot be resilient or expandable but may be made rigid or inflexible. Ifthe fluid is incompressible, then the fluid capacitance should beelastically deformable or should have a free surface. Typical fluidcapacitances are provided by pressure-loaded, flexible diaphragms whichseparate two fluids of different densities and elastically deformabletanks or containers.

It is assumed, for the purpose of explanation, that the fluid employedin the sensor 26 is incompressible, for example, water, and that thecapacitance 138 includes a cylindrical casing 139 and a circular,flexible diaphragm 140 for allowing variations in the capacitance of theupper chamber 137 resulting from increases and decreases in waterpressure in the tube 136. The peripheral edges of the diaphragm aresealed to the inner walls of th casing 139 so that fluid in the upperchamber 137 is kept separated from fluid in the lower chamber 141 of thecasing 139. The fluids on either side of the diaphragm 140 should havedifferent compressibility, the fluid having greater compressibilitybeing disposed in the lower chamber 141. Assuming that water is to beused as the working fluid in the sensor 26, a compressible fluid, suchas air, may be used in the lower chamber 141. The position of thediaphragm 140 and the volume of the chamber 137 vary in accordance witha variation in pressure against the opposite face of the diaphragm, thevolume of the chamber 137 being governed by the flexibility of thediaphragm 140 and the relative pressures applied against the diaphragmby the fluids in each chamber.

If the water pressure in the upper chamber 137 increases, the diaphragm140 expands downwardly into the lower chamber 141 compressing the airinto a smalier volume and thereby increasing the volume of the upperchamber 137. Conversely, a reduction in water pressure in the upperchamber produces an upward expansion of the diaphragm by expansion ofthe air in the lower chamber 141, thereby decreasing the volume of theupper chamber 137.

An output tube 142 extends from an opening in the casing 139 into theupper chamber 137 of the fluid capacitance 138 and supplies fluid pressure signals to the control nozzle 148 of the fluid amplifier A2. Thenozzle 148 provides a resistance to flow from the upper chamber 137 aswell as a control nozzle for the amplifier A2.

The tubes 136 and 142 and the upper chamber 137 receive fluid at apredetermined constant reference pressure from a supply 69 by means of afilter 69a, a tube 143 and a nozzle 144. The end of the nozzle 144 isadmitted into an opening 145 formed in circular end wall 146 of thecapacitance 138, the nozzle serving as a resistance to flow from thetube 143.

The resistances and 148 formed by constrictions at the ends of the tubes136 and 142, respectively, and the resistance offered to flow by thenozzle 144 cooperate to permit the development of a region of relativelyhigh pressure defined between these resistances and the diaphragm 140,thereby providing a capability of continuous outflow from the ports 133and from the nozzle 148, even though the ports and the nozzle 148 areheavily backloaded. Thus, even if relatively large static pressures areencountered by the ports 133, flow continues to egress from these portspreventing the ingress of flow from the surrounding fluid medium intothe sensor 26. Ordinarily, continuous outflow is necessary in order toprevent the introduction of extraneous material into the sensor from animpure ambient fluid medium. Fluctuations in back pressure developed inthe tube 136 are a function of the magnitude of instantaneous staticpressures acting on the ports 133, the back pressure in the tube 136increasing as the static pressure sensed by the probe 132 increases.

The resistances provided by constrictions 135 and 148 acting togetherand in conjunction with the capacitance of the fluid capacitance 138establish a resistance-capacitance time constant for the sensor 26 whichmay be of any desired value. This feature is of primary importance sinceit is not intended that the sensor cause high frequency pressure signalsto be issued from the nozzle 148. High frequency pressure variationsmay, for example, be produced by a choppy seaway in which the foil 10 ismoving, or by minor high frequency perturbations in pressure of thefluid medium surrounding the sensing ports of the probe 132. Since thepressure build-up in the tube 136 is dependent upon theresistance-capacitance time constant of the sensor 26, the sensor can bedesigned so as to attenuate or damp out undesired high frequencypressure fluctuations or variations. Fluid pressure signal attenuationmay be easily effected by adjusting the flexibility of the diaphragm140, since this also adjusts the capacitance of the fluid capacitance138 and therefore the time constant of the sensor.

The source 69 and filter 69a may be housed in the craft 13 and the tube143 encased in a channel formed in the strut 11 so that the fluidcapacitance 138 receives only filtered fluid from the tube 143. Asmentioned previously, the pressure signals from the depth sensor 26 arecompared with the prescribed depth command signal which issues from thesource 27 and hence from the control nozzle 149 positioned opposite thecontrol nozzle 148. The displacement of the power stream issuing fromthe power nozzle 91 is determined by the relative magnitudes of thepressure differentials which exist as a result of fluid stream issuingfrom control noules 148, 149, 72 and 73. Thus, signals from the lift andstatic pressure sensors are combined in the amplifier A2 with thecommand depth signal to provide an amplified output signal thatmaintains the depth and lift of the foil 10 constant as it moves throughthe medium 14.

In order to stabilize a craft in its medium, it may be desirable toemploy pitch and roll rate sensors in the control system. If fore andaft hydrofoils are employed and both are servoed, pitch rate signals maybe applied in differential relationship to the controls for the fore andaft hydrofoils to control pitch. If two transversely aligned foils areservoed, then a roll rate signal of a given sense is applied to one orboth foils.

A roll rate signal may be employed for control of roll only if twotransversely aligned foils are independently servoed. Roll rate signalsare applied differentially to the controls for the two foils so that, asangle of attack of one foil is increased, the angle of attack of theother is decreased, thus tending to counter the foil movement.

Referring again to FIGURES 1 and 2, a pitch rate transducer designatedas 28a and a roll rate transducer 28b are provided and may be housed inthe craft 13 or strut 11. The pitch rate transducer 28a supplies fluidcontrol signals to the control nozzles 150 and 151, respectively, ofamplifier A3 whereas the roll rate transducer 28b supplies control fluidsignals to the control nozzles 152 and 153 of that amplifier. The pitchand roll rate transducers may be of any suitable conventional design andare preferably of a pure fluid type as disclosed in (1) the Sc. D Thesisof Forbes T. Brown, entitled Pneu matic Pulse Transmission withBi-stable Jet Relay Reception and Amplification, Department ofMechanical Engineering, M.I.T., May 1962, and (2) ASTIA Publication No.AD277470. The transducers are oriented with their axes of rotation atright angles so that the pitch and the roll of the craft 13 are sensedand the fluid signals issuing from each of these transducers aresupplied as control streams to effect displacement of the power streamissuing from the power nozzle 92 of the summing amplifier A3, therebydisplacing the power stream relative to the output passages 80 and 81 inaccordance with summation of the presure signals received. The output ofthe tubes 80 and 81 is pressure amplified by the amplifiers A4 and AS soas to eflect the required pivotal movement of the foil about the pin 12by means of the servo unit 19. The directional senses of pitch and rollare indicated by the plus and minus signs in FIGURE 2, and those workingin the art will be able to couple the transducers 28a and 28b to thecontrol nozzle of the amplifier A3 of each foils pure fluid controlsystem so that the angle of attack of each foil 10 is alteredappropriately to correct for variations in pitch and roll of the craft13. In control of roll in a system employing two transversely ali-gnedfoils, the signals developed by the roll rate transducer 28b are appliedin opposite senses to their corresponding amplifiers A3. Thus, the liftdeveloped by one foil is reduced while the lift developed by the otherfoil is increased, thus tending to counter the roll movement whilemaintaining total lift constant. The transducers 28a and 28b may beeither housed in the craft 13 or embodied in the strut 11.

To summarize briefly, the hydrofoil control system utilizes fluidelements which function with a minimum or no moving parts, the elementsbeing arranged in a fluid circuit to sense, compute and ultimatelycontrol the angle of attack of one or more of the foils supporting acraft for movement in a liquid medium. The basic computer circuitincludes five pure fluid analog-type amplifiers A l, A2, A3, A4, and AS,the amplifiers A1A5 inclusive being controlled by fluid signals fromlift and depth sensors 20 and 26, respectively, depth command signalsfrom the source 27, and pitch and roll rate signals from the transducers28a and 28b. Each pure fluid lift sensor 20 provides an output fluidsignal which is proportional to the lift developed by its associate foil10 so that instantaneous changes in the medium local flow conditions andfoil speed can be sensed and the angle of attack of the hydrofoilaltered such that the foil 10 develops a substantially constant butcontrollable lift force during movement. In addition, depth commandsignals provided by the source 27 are compared or summed with thesignals from the depth sensor 26 in the pure fluid amplifier A2, thesource 27 issuing preselected running depth reference signals for thefoil 10 in the medium 14. Thus, the angle of attack of a foil 10 may bechanged in accord ance with variations in depth of the foil 10 in themedium 14 from the preselected running depth. These signals areamplified and summed with signals dependent upon the pitch and roll rateof the craft 13, in the amplifier A4, and the differential pressureoutput of the amplifier A4 is 14 amplified in the fluid amplifier A5.The differential pressure output signals which issue from the outputpassages of the amplifier A5 can be expressed by the following equation:

i p+ 2 r+ 3 4 Po K is the depth command signal;

0,, is the pitch rate of the craft 13;

0, is the roll rate of the craft 13;

L is the lift of the foil 10',

h is the depth of the foil 10 in the medium 14.

K, C C C C are constants appropriate to the particular foil 10 and itssupport location relative to the vehicle center of gravity.

The output signal of the pure fluid amplifying system A1 is amplified bythe pressure amplifiers A2, A4 and A5 and the pressure signals from theamplifier A3 are amplified by the amplifiers A4 and A5 to provide apressure signal to effect adjustment of the foil 10 by actuation of theservo unit 19.

In accordance with a second embodiment of the present invention, andreference is made to FIGURE 6 of the drawings, a foil 10a, also of thesubcavitation type, is provided with a pair of opposed vents 154 and 155into which fluid flow from the output passages 30 and 31 issues to theupper and lower surfaces of the foil, respectively. In this system, thedesired parameter is not pressure but fluid flow and therefore, the purefluid amplifiers which comprise the control system 21 should be designedto provide maximum flow gain rather than maximum pressure gain. Thoseworking in the pure fluid amplifier art will be able to designamplifiers having this characteristic. The actions of the fluid flowsissuing from the vents 154 and 155 produce an opposite reaction due to acombination of momentum exchange and change in the pressure distributionon the surface of the foil 10a, tending to pivot the foil 10a about theconnecting pin 12. The foil pivots in a clockwise direction when therate of fluid flow from the output passage 31 and the vent 154 exceedsthat issuing from the output passage 30 and the vent 155, and pivots thefoil in a counterclockwise direction when the flow from the passage 30exceeds that in the output passage 31. In this system, no movingmechanical elements are needed to adjust the angle of attack of the foil10a, only the working fluid employed in the control system beingutilized for this purpose.

In addition to the momentum forces produced by flow from the vents 154and 155, the pressure distributions of the fluid flowing along andagainst the upper and lower surfaces of the foil 10a are modified by theflow from the vents 154 and 155. For example, flow from the vent 154increases the pressure distribution across the upper surface of the foil10a between the connecting pin 12 and the trailing edge of the foil 10aand the resulting increase in the pressure distribution tends to rotatethe trailing edge of the foil 10a clockwise about the pin 12 so as toaid the momentum forces developed by flow from the vent 154.Correspondingly, flow from the port 155, in addition to producing amomentum force that tends to pivot the foil 10a counterclockwise withrespect to the pin 12, also increases the pressure distributiondownstream of the pin 12 on the lower surface of foil 10a thereby actingin conjunction with the momentum forces caused by flow from the vent 155to rotate the foil counterclockwise about the pin 12.

FIGURE 7 of the drawings illustrates a system for maintaining constantlift of a supercavitating foil 10b employing fluid jet flap control. Thefoil is formed with a substantially straight upper surface 157 and aconcave lower surface 158. As illustrated in FIGURES 2 and 7, the fluidcontrol system 21 receives fluid control signals from the lift sensor 26attached to the lower surface 158 of the foil 10b and positioned underand forward of the leading edge of the foil, and from the depth sensorand depth command signal sources 26 and 27 and as well as from pitch androll rate transducers generally designated by the numeral 28 (whereappropriate). A main intake nozzle 160 is formed in the foil 10b andcommunicates through the lower surface 158 of the foil with the fluid ofthe medium 14. The fluid introduced into nozzle 160 is at some elevatedvelocity during movement of the foil through a liquid medium 14. Theintake nozzle 16!] converges as shown, so that the fluid stream whichegresses from the nozzle 160 is constricted and acts as a power streamfor subsequent displacement by control stream flow issuing from theoutput passages 30 and 31 of the amplifying system 21 in an interactionchamber 164 provided in the foil 10b. A supplementary source of fluidfor the interaction chamber 164 may be supplied from a nozzle 161 whichis positioned in the main intake nozzle 160 to issue fluid toward thedownstream end of that nozzle, the nozzle 161 being connected by meansof a tube 162 to a source of pressurized fluid 163 housed in the craft13. The tube 162 may be housed in a channel formed in the strut 11. Ifdesired, the main intake nozzle 160 may be eliminated, and the nozzle161 may supply all the power stream fluid into the interaction chamber164 from the source 163. The interaction chamber 164 communicates with apair of outlets 166 and 167 located downstream of the chamber 164, theoutlet 166 discharging fluid received thereby from the trailing end ofthe hydrofoil 10b. Fluid issuing from the outlet 167 on the other handacts as a jet flap and raises the pressure distribution of fluid alongthe lower surface 158, thereby increasing the lift of the foil 10b.Because of the supercavitating effect which is developed along the uppersurface 157 of the foil 10b and the liquid medium through which the foilis moving, a region of lower pressure is created along the upper surface157 and this lower pressure region acts to aid the upward movement ofthe foil 10b, as viewed in FIGURE 7.

The displacement of the fluid issuing from the nozzle 160 and/or thenozzle 161 in the interaction chamber 164 by flow from the passages 30and 31 is amplified since the configuration provides an additional purefluid amplifyiug system. Fluid issuing from the pasage 31 effectsdisplacement of the power stream in the chamber 164 into the outlet 167so that an increase of lift force is developed by the foil 10b, whereasdisplacement of the power stream by fluid issuing from the pasage 30into the outlet 166 produces minimum lift, primarily since the pressuredistribution along the lower surface 158 of the foil is not raised byfluid issuing from this outlet.

The conditions for control of the foil or foils are quite differentduring take-off and crash diving; that is, during rapid ascending ordescending movement of the craft 13 in said fluid medium 14, from theconditions during normal cruising. During normal cruising, the requiredchange of the lift coefficient of the foil is approximately :0.3.However, during take-olf and crash diving, the lift coefiicient changemay be between 21.2 and $1.8. Since the control system is designedprimarily for cruising conditions, the system normally cannotaccommodate input signals nor produce output signals or foil positioningof the magnitude required for the aforesaid special conditions.Therefore, in accordance with another feature of the present invention,special provision is made for control of the lift coefficient of thefoil during take-off and crash diving. To provide a specific example ofa type of control for these latter conditions, fluid-controlled,mechanical flow spoilers are employed.

Referring now specifically to FIGURE 8 of the accompanying drawings,there is illustrated a fixed position subcavitating type of foildesignated generally by the numeral 10c having pure fluid flow controlof lift during normal operations. The foil 10c is formed bysymmetrically tapering upper and lower surfaces 168 and 169,respectively. The control system for controlling the lift of the foil10c includes the lift sensor attached to the lower surface 169 andextending forwardly of the leading edge of the foil, the depth sensorand depth command signal sources 26 and 27, respectively, and roll andpitch transducers 28, these monitoring elements supplying fluid controlsignals for the fluid control system 21. The tubes or passages 30 and 31receive the output flow from the amplifier 21 as described previously.The foil 10c is provided with a nozzle 170 extending axially through thefoil, the nozzle tapering to a nozzle orifice 171 for issuing aconstricted fluid stream into an interaction chamber 172 formed in theairfoil. A pair of output passages 173 and 174 are positioned downstreamof the chamber 172 and receive fluid issuing therefrom. A nozzle 175 ispositioned to issue supplementary flow to the orifice 171, the nozzlebeing connected to a tube 176 which is housed in the strut 11 and whichreceives fluid from a source of constant pressurized fluid 177 supportedin the craft 13. If desired, the intake nozzle 170 may be dispensed withso that the interaction chamber 172 receives flow solely from the source177 by means of the nozzle .175. Flow issuing from the output passages30 and 31 effects displacement of the constricted fluid stream orstreams which issue into the interaction chamber 172 relative to theentrance to the outlets 173 and 174 so that the flow received by theseoutlets is a function of the displacement of the power stream in thechamber 172 by flow from the passages 30 and 31, respectively.

Fluid flow from the outlet 173 increases the pressure distribution alongthe upper surface 168 of the foil 10c thereby decreasing the lift of thefoil, whereas fluid flow issuing from the outlet 174 increases thepressure distribution along the lower surface 169 of the foil 10c,thereby increasing the lift of the foil 10c.

A pair of mechanical flow spoilers 180 and 181 are located adjacent theupper and lower surfaces 168 and 169, respectively, of the foil 10c. Theflow spoilers are designed to be actuated selectively for movementoutwardly of the surfaces 168 and 169 by fluid pressure from outputtubes 182 and 183, respectively, of a pure fluid amplifier A6, FIGURE 2,during take-off and crash divmg.

Control nozzles 186 and 187 and the tubes 188 and 189 of the amplifierA6 are connected, respectively, through a T connection (see intersectionof passages 118 and 122 of FIGURE 4) with the output passages or tubes30 and 31.

The amplifier A6 is designed to be insensitive to small signals of thelevels encountered in normal control of the foils during cruising. Thisis accomplished by making a center output passage 184 of the amplifiersulficiently wide that insufficient fluid is deflected to passage 182 or183 to operate the flow spoilers in response to normal control signals.However, if the power stream of the amplifier A5 is substantially fullydeflected, the control signals applied to control nozzles 186 and 187 ofamplifier A6 are suflicient to direct enough output flow to one or theother output passage 182 or 183 to operate its associated spoiler.Manual or automatic valves (not shown) may be incorporated in the tubes182 and 183, the valves normally closing both tubes to flow from theamplifier A6 and being employed to open the tubes to permit takeoff andcrash diving. During the extreme operating conditions of craft take-offand crash diving, the pressure from the tubes 182 or 183 drasticallychanges the lift of the foil 10c by means of the mechanical flowspoilers.

During take-off, for example, the depth sensor 26, FIG- URE 2, sensesmaximum depth and therefore develops near maximum static pressure whichmay cause the pressure of fluid in the control nozzle 148 of theamplifier A2 to override the pressure signal in the control nozzle 149as established by fluid issuing from the depth command source 27. Thiscondition may cause near maximum displacement of the power stream in theamplifier A2 with the output tube 75 receiving a considerably greaterflow than the tube 74. As a result, the amplifiers A4 and A5 may besaturated by the flow from the connecting tubes or passages and thecontrol nozzle 86 of the amplifier A will effect displacement of thegreater proportion of the flow into the output passage 89 of thatamplified. Since the amplifier A5 may be near saturation, its outputpassage 89 will deliver a substantial signal to control nozzle 187 ofamplifier A6. As a result, the power stream issuing from the powernozzle 191 of the amplifier A6 is displaced into the output tube 183 andflow from the tube 183 drives the spoiler 181 outwardly from the lowersurface 169 of the foil c, thereby increasing the pressure distributionalong that surface upstream of the spoiler 181, the increase in pressureincreasing the lift of the foil 10c to a value not normally obtainablewith a foil of the specific design employed.

During a crash dive, the depth command signal source 27 may be manuallyoperated so that a relatively large magnitude output pressure signal isreceived by the control nozzle 149 of the amplifier A2 to which thesource 27 is connected. In this case, the overriding pressure signalfrom the source 27 displaces the power stream issuing from the nozzle 91so that the output tube 74 receives the greatest proportion of fluid,the fluid received being great enough when transmitted through theamplifiers A4 and A5 to saturate the amplifier A5 and by issuing fromthe control nozzle 87 causes strong fluid signals to enter the outputtube 188 so as to displace the power stream issuing from the powernozzle 191 of the amplifier A6 sufficiently that it enters into theoutput tube 182. Fluid from the output tube 182 actuates the spoiler 180so that the spoiler is moved ouwardly of the upper surface 168 of thefoil 10c thereby increasing the pressure distribution along that surfaceupstream of the spoiler 180 and decreasing the lift of the foil 10c.

It will be evident that the systems illustrated in FIG- URES 6, 7 and 8at least partially utilize the output flow of the fluid control system21 to effect the lift of the foil by changing pressure effects on thesurfaces of the fixed foil, whereas in the embodiment illustrated inFIGURE 1, the lift control is achieved by varying the angle of attack ofthe foil. In the systems of FIGURES 6, 7 and 8, flow rather pressure isthe primary desired output parameter of the computer system. Theparticular ampli fiers forming the control system 21 illustrated inFIGURE 2 are more efficient in ampilfying pressure control signals thanin amplifying flow control signals. Those working in the art, however,will be able to replace the pressure amplifiers A1-A6, inclusive, withamplifiers which more efficiently amplify fluid flow signals if resortto that expedient is deemed desirable for higher efficiency in thecomputing operation.

As has been previously indicated, the foil lift control system of thepresent invention may be employed with various numbers and types of foilarrangements. Referring specifically to FIGURE 9 of the accompanyingdrawings, there is illustrated a hydrofoil craft 200 employing threeindependently servoed hydrofoils.

The craft 200 is provided with two transversely aligned struts 201 and202 aligned transversely of the longitudinal centerline of the craftpositioned toward the bow thereof. Two hydrofoils 204 and 205 areattached to the struts 201 and 202, respectively. A third strut 203positioned toward the stern of the craft 200 is positioned symmetricallywith respect to the longitudinal centerline thereof. A foil 206 issecured to the strut 203.

Each of the foils 204, 205 and 206 is provided with a lift sensor 207,208 and 209, respectively, and a depth sensor (not illustrated) whichmay be of the type illustrated in FIGURE 5. In such a foil system, fluidpitch rate signals are applied in one sense to control systems (seeFIGURE 2) for the foils 204 and 205 and in a differential sense to thefoil 206. Fluid roll rate signals are applied differentially to thecontrol systems of the foils 204 and 205.

Such a system, including lift, depth, roll and pitch rate controlservoes the foils such that the craft 200 becomes a stable platform, adesirable result particularly where the craft 200 is to be employed forattack purposes.

FIGURE 9 illustrates two forward foils but it is to be understood that acentered, single, large foil may be employed. In such case, the frontfoil would be a V-shaped surface piercing on the suitable foil. Rollrate cannot be controlled by the foils in such a case although pitchrate may be. Further, if the front two foils are not servoed, twosurface-piercing or ladder-type foils would be employed.

While I have described and illustrated several specific embodiments ofmy invention, it will be clear that variations of the details ofconstruction which are specifically illustrated and described may beresorted to without departing from the true spirit and scope of theinvention as defined in the appended claims.

What I claim is:

1. A system for controlling the position of a foil or the like in afluid medium comprising sensing means for monitoring variations in theposition of the foil relative to a reference plane and for producingfluid output signals corresponding to the variations monitored; at leastone pure fluid amplifier coupled to said sensing means, said amplifierincluding a power nozzle for issuing a constricted power stream, pluraloutput passages located downstream of said power nozzle for receivingfluid therefrom, and a pair of control nozzles angularly disposed withrespect to said power nozzle for comparing substantially opposed controlstreams issuing in interacting relationship with said power stream forelfecting displacement of the power stream relative to said outputpassages; adjustable means connected to one of said control nozzles forproviding a predetermined fluid bias signal to said amplifiercorresponding to the desired position of the foil relative to saidreference plane, the other control nozzle of said pair connected to saidsensing means to receive the fluid output signals issuing therefrom, thedifferential fluid signal issuing from said output passages of saidamplifier resulting from displacement of the power stream correspondingto variations in foil position from said predetermined plane; and meansfor receiving the differential fluid signals issuing from said outputpassages and varying the position of the foil relative to said plane inaccordance with the differentials in fluid signals received.

2. The system as claimed in claim 1 wherein all parts forming the saidsensing means remains stationary relative to each other during theposition monitoring operation.

3. A system for controlling the position of a foil or the like in afluid medium comprising plural position sensing means attached to thefoil for measuring the position of the foil relative to various positionreferences and producing fluid output signals corresponding to saidmeasurements; staged plural pure fluid amplifiers for summing andsuccessively amplifying the fluid output signals from said sensingmeans, each amplifier stage including a power nozzle for issuing aconstricted power stream into the amplifier, plural output passageslocated downstream of said power nozzle for receiving fluid therefrom,and at least two pairs of substantially opposed control nozzlesangularly located with respect to said power nozzle for issuingsubstantially opposed control streams in interacting relationship withthe power stream issuing from said power nozzle for effectingdisplacement of the power stream relative to said output passages; theoutput passages of one stage being connected to one pair of controlnozzles of a succeeding stage; means connected to one control nozzle ofthe other pair of control nozzles of each amplifier for providing apredetermined fluid bias signal to the power stream, the other controlnozzle of said other pair of control nozzles of each amplifier coupledto said sensing means and receiving variable fluid signals therefrom,the variable fluid signals issuing from said control nozzles, the fluidbias signals, and the output fluid signals from a preceding amplifierstage causing displacement of the power stream in each amplifier inaccordance with the variation in the position of the foil as monitoredby said sensing means; and means receiving the fluid signals issuingfrom the last amplifier stage for changing the position of the foil inaccordance with the fluid signals received.

4. A system for controlling the position of a foil or the like in afluid medium comprising plural position sensing means for monitoringvariations in the position of the foil from a predetermined referenceaxis, each sensing means producing fluid output signals corresponding tothe variations monitored; at least a pair of pure fluid amplifiers, eachamplifier including a power nozzle for issuing a defined power stream inthe amplifier, plural output passages located downstream of said powernozzle for receiving fluid streams therefrom; one amplifier of said pairhaving a pair of opposed control nozzles angularly positioned withrespect to said power nozzle for issuing substantially opposed controlstreams in interacting relationship with the power stream so as toeffect displacement of the power stream relative to said outputpassages, means connected to one of said control nozzles for providing afirst predetermined fluid bias signal to said one amplifier, the othercontrol nozzle of said pair connected to one of said position sensingmeans so as to receive the fluid signal output therefrom; the otheramplifier of said pair of amplifiers having first and second pairs ofsubstantially opposed control nozzles, the first pair of control nozzlesconnected to the output passages of said one amplifier for receivingfluid output signals therefrom; means connected to one nozzle formingthe second pair of said control nozzles for supplying a secondpredetermined fluid bias signal to said other amplifier; the othercontrol nozzle of said second pair connected to receive fluid signalsfrom another position sensing means, the displacement of the powerstream in said other amplifier corresponding to a summation of fluidsignals received by said first and second pairs of control nozzles; andmeans positioned to receive the fluid signals issuing from the outputpassages of said other amplifier for changing the position of the foilin accordance with the fluid signals received.

5. A system for controlling the position of a foil or the like in afluid medium comprising first and second sensing means for monitoringvariations in two planes of the position of the foil with respect topredetermined reference planes, said sensing means producing fluidoutput signals corresponding to variations monitored thereby; a pair ofpure fluid amplifiers for receiving and amplifying the output signalsfrom said sensing means, each amplifier including a power nozzle forissuing a defined power stream, plural output passages locateddownstream of the power nozzle for receiving fluid streams therefrom,one amplifier of said pair having a pair of substantially opposedcontrol nozzles angularly disposed with respect to the power nozzle forissuing control streams in interacting relationship with the powerstream issuing from that power nozzle, said first sensing meansconnected to said control nozzles for providing fluid control signalsfor said one amplifier corresponding to the variations of foil positionabout one plane; the other amplifier of said pair including first andsecond pairs of substantially opposed control nozzles angularly disposedwith respect to said power nozble for effecting displacement of thepower stream relative to the output passages of said other amplifier,the first pair of control nozzles connected to the output passages ofsaid one amplifier so as to receive and amplify the fluid signalsissuing from said one amplifier; means connected to one nozzle of thesaid second pair of said control nozzles for supplying a predeterminedfluid bias signal thereto, the other control nozzle of said second pairof control nozzles connected to the second sensing means for re ceivingfluid signals therefrom corresponding to variations of foil positionabout the second plane, said other amplifier summing and amplifyingfluid signals received by the control nozzles by displacement of thepower stream in said other amplifier; and means formed in said foil forchanging the position of the foil in accordance with the fluid signalsreceived from the output passages of said other amplifier.

6. The system as claimed in claim 5 wherein said first sensing meanscomprises a fluid lift sensor for sensing the lift forces received bythe foil during movement thereof.

7. The system as claimed in claim 5 wherein said second sensing meanscomprises a fluid depth sensor for sensing the average running depth ofthe foil in the medium, and wherein said means for supplying apredetermined fluid bias signal to said one control nozzle of saidsecond pair of control noules comprises means for producing a fluidoutput signal corresponding to a preselected running depth of the foilin the medium.

8. The system as claimed in claim 5 wherein additional pure fluidamplifiers are coupled to receive fluid from the output passages of saidother amplifier for further amplifying the output fluid signalstherefrom, and wherein the output from said additional pure fluidamplifier supplies amplified fluid signals to control said means forchanging the position of the foil in the medium.

9. The system as claimed in claim 8 wherein said additional pure fluidamplifiers include plural opposed control nozzles to reflectingamplified displacement of a power stream flowing in each additionalamplifier; and wherein further sensing means for monitoring variationsin the position of the foil with respect to a third plane is providedand issues output fluid signals corresponding to such variationsmonitored, said further sensing means connected to one control nozzle ofone of said additional pure fluid amplifiers.

10. The system as claimed in claim 5 wherein the means for changing theposition of the foil in accordance with the fluid signals receivedthereby comprises plural outlet passages formed in said foil, saidpassages being angularly disposed with respect to each other and withrespect to the direction of movement of the foil in the medium.

11. The system as claimed in claim 10 wherein the foil is of thesubcavitating type.

12. The system as claimed in claim 10 wherein the foil is of thesupercavitating type.

13. The system as claimed in claim 10 wherein the foil is mounted forpivotal movement in the fluid medium, and wherein said outlet passageissue fluid streams outwardly from the foil downstream of the point ofpivotal movement so as to effect pivotal movement of the foil.

14. A system for controlling the lift of a foil in its fluid mediumcomprising a strut, means for pivotally mounting said foil on saidstrut, fluid sensing means mounted on said foil for determiningdeviation from a desired value of lift generated by the position of saidfoil in its fluid medium which lift may be controlled by changing angleof attack of said foil, said means for sensing developing a differentialfluid signal which varies as a function of deviation of said lift fromsaid desired value, and means for applying said fluid signal to saidfoil to produce rotation of said foil to reduce said deviation from saiddesired value.

15. A system for controlling the lift of at least one foil of amultiple-foil hydrofoil craft in its fluid environment comprising astrut for supporting said at least one foil, means for pivotallymounting said fail on said strut, said foil having a hollow chamberformed interiorly thereof, a vane rigidly secured to said strut anddividing said chamber into two isolated regions, sensing means fordetermining deviation from a desired value of at least one parametereffected by the position of said foil in its environment which parametermay be controlled by changing the lift of said foil, said sensing meansdeveloping a pair of fluid signals which vary differentially as afunction of deviation of said parameter from said desired value, andpassages located in said foil for applying said signals 21 to said twoisolated regions of said chamber in such a sense as to cause said foilto rotate in a direction to correct said deviation in the measuredparameter.

16. The system as claimed in claim 15 wherein said sensing meanscomprises a lift sensor positioned forwardly of said foil.

17. A system for controlling the lift of a foil in its fluid environmentcomprising [a strut,] a foil, means for supporting said foil [rigidlysecured to said strut], said foil having a pair of passages locatedtherein and extending through surfaces thereof, one of said passagesextending through a lower surface of said foil adjacent the trailingedges thereof, sensing means for determining deviation from a desiredvalue of at least one parameter effected by the position of said foil inits enviroment which parameter may be controlled by changing the lift ofsaid foil, said sensing means developing a pair of fluid signals whichvary differentially as a function of deviation of said parameter fromsaid desired value, and means for applying said fluid signals each to adifferent one of said passages in such a sense as to change the lift ofsaid foil in the sense determined by at least one of said fluid signals.

18. A foil control system for positioning a foil in its environmentcomprising means for sensing lift of said foil and producing a firstfluid signal indicative thereof, means for measuring the depth of saidfoil relative to a commanded depth and producing a second fluid signalindicative thereof, fluid amplifier means for combining said signals andproducing a further fluid flow signal which is a function of both saidfirst and second fluid signals and means responsive to said furtherfluid signal for altering the lift of said foil as a function of saidfurther signal.

19. The system as claimed in claim 18 wherein said means for combiningcomprises at least one fluid amplifier including means for issuing apower stream of pure fluid and means for deflecting said stream as afunction of said first and sec-nd signals to produce said further flowsignal.

20. The system as claimed in claim 19 wherein said means for alteringthe lift of Said foil includes a fluid amplifier having a power nozzlefor issuing a power stream of fluid, said nozzle including a passagesupplied with fluid from said environment due to movement of said foiltherethrough.

21. A system controlling the position of a moving foil or the likesubmerged in a fluid medium comprising depth sensing means formonitoring variations in the position of the foil in said mediumrelative to a reference plane corresponding to the average running depthof said foil and for producing fluid output signals corresponding to thevariations monitored; at least one pure fluid amplifier coupled to saidsensing means, said amplifier including a power nozzle for issuing aconstricted power stream, plural output passages located downstream ofsaid power nozzle for receiving fluid therefrom, and a pair of controlnozzles angularly disposed with respect to said power nozzle forcomparing substantially opposed control streams issuing in interactionrelationship with said power stream for effecting displacement of thepower stream relative to said output passages; adjustable meansconnected to one of said control nozzles for providing a predeterminedfluid bias signal to said amplifier corresponding to the desiredposition of the foil relative to said reference plane, the other controlnozzle of said pair connected to said sensing means to receive the fluidoutput signals issuing therefrom, the differential fluid signal issuingfrom said output passages of said amplifier resulting from displacementof the power stream corresponding to variations in foil position fromsaid predetermined plane, and means for receiving the differential fluidsignal issuing from said output passages and varying the position of thefoil relative to said plane in accordance with the differentials influid signals received.

22. A system for controlling a multiple-foil craft in its fluidenvironment wherein said craft has two transversely aligned foils and afurther foil disposed aft of said two foils, a strut separatelysupporting each of said foils, a separate sensing means for each of saidfoils for determining deviation from a desired condition of at least oneparameter that is effected by the position of said foil in its fluidenvironment and which condition of said parameter may be controlled bychanging the lift of said foil, each of said sensing means developing afluid signal which varies as a. function of variations of saidparameter, separate control means for each of said foils including saidfoil for changing the lift thereof as a function of said signal, a pitchrate measuring means for generating two pitch rate fluid signals whichvary differentially with pitch rate of said craft, means for applyingone of said pitch rate signals to said control means of said two foilsand for applying the other of said pitch rate signals to said furtherfoil, a roll rate measuring means for generating two roll rate fluidsignals which vary differentially with roll rate of said craft, andmeans for applying one of said roll rate signals to one of said twofoils and for applying the other of said roll rate signals to the otherof said two foils.

23. The system as claimed in claim 22 wherein each of said sensing meansincludes a depth sensor and a lift sensor.

24. A system for controlling the lift of at least one foil of a multiplefoil hydrofoil craft in its fluid environment comprising a [strut] foil,means for [securing] supporting said foil [to said strut], sensing meansfor determining deviation from a desired condition of at least oneparameter that is effected by the position of said foil in its fluidenvironment and which condition of said parameter may be controlled bychanging the lift of said foil, said sensing means developing a fluidsignal which varies as a function of variations of said parameter,control means including said foil for changing the lift thereof as afunction of said signal, flow spoilers disposed in said foil and mountedfor controlled outward movement therefrom in response to said fluid flowsignal, and means for directing fluid to said flow spoilers to produceextension of at least one of them in response to said fluid signal onlyabove a predetermined magnitude.

25. The system of claim 21 wherein is further provided a fluid liftsensor for monitoring the lift forces received by said foil and forproducing other fluid output signals corresponding to the lift forcemonitored, said amplifier including a second pair of control nozzlesconnected to said lift sensor to receive the fluid output signalsissuing therefrom whereby said differential fluid signal is dependentupon said lift forces monitored.

26. The system of claim 25 wherein said means for receiving thedifferential fluid signals and varying the position of said foil inresponse thereto includes a strut for supporting said at least one foil,means for pivotally mounting said foil on said strut, said foil having ahollow chamber formed interiorly thereof, a vane rigidly secured to saidstrut and dividing said chamber into two isolated regions, and passageslocated in said foil for applying said signals to said two isolatedregions of said chamber in such a sense as to cause said foil to rotatein a direction to correct said deviation in the measured parameter.

27. The system of claim 26 wherein said pure fluid amplifier is locatedinteriorly of said foil.

28. The system of claim 15 wherein said system includes pure fluidamplifier means for amplifying said pair of signals and for combiningsame for delivery to said passages, said amplifier means being locatedinteriorly of said foil.

29. The combination according to claim 17 wherein said means forapplying said fluid signals comprises pure fluid amplifier means havingoutput channels connected to said pair of passages to applydifferentially varying signals thereto, said fluid amplifier havingmeans for issuing a 23 stream of fluid toward said output channels andmeans responsive to said sensing means for varying flow to said outputpassages as a function of deviaion from a desired value of said at leastone parameter.

30. The combination according to claim 17 wherein said sensing meanscomprises means for sensing the lift of said foil.

31. The combination according to claim 17 wherein said sensing meanscomprises means for sensing the rate of rotation of s id foil about anaxis thereof.

32. The combination according to claim 17 wherein said sensing meanscomprises means for sensing the depths of said foil in its fluidenvironment.

References Cited The following references, cited by the Examiner, are ofrecord in the patented file of this patent or the original patent.

UNITED STATES PATENTS 3,103,197 9/1963 Von Schertel 1l466.5 3,137,4646/1964 Horton 244-78 FOREIGN PATENTS 549,266 10/ 1956 Italy. 882,517 7/1953 Germany.

ANDREW H. FARRELL, Primary Examiner.

